We report b-axis electrical conductivity data for TSeF-TCNQ single crystals from 12 to 300 K under hydrostatic pressures up to 9 kbar. The single anomaly visible in the conductivity at 29 K and the low temperature conductivity gap rise under pressure at the same rate of ∼ 6% kbar-1. It has been found that the pressure dependence of the metal-insulator phase transition is qualitatively consistent with a mean field formulation of the Peierls transition. A Gruneisen constant of 0.64 for TSeF-TCNQ has been derived from this pressure study together with recent optical and compressibility investigations. The pressure dependence of the conductivity anisotropies at room temperature in TSeF-TCNQ and TTF-TCNQ are reported. The magnitude of the anisotropies in the two compounds are found to be essentially the same. The striking result, however, is that the anisotropies in both compounds are found to be independent of pressure up to 9 kbar. © 1977.